Development of a Surrogate Virus Neutralization Test for Middle East Respiratory Syndrome Coronavirus

Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is the causative agent of a highly infectious viral respiratory illness with a high mortality rate of over 30%, and the current medical system has no licensed vaccines or specific antiviral treatments for the disease, making it especially threatening to the public health. Therefore, to support the MERS-CoV vaccine and therapeutics development, we are developing a surrogate virus neutralization test (sVNT) in the format of a competitive enzyme-linked immunosorbent assay (ELISA) to detect the immunodominant neutralizing antibodies in the humoral serum samples. To date, we have expressed Human Dipeptidyl Peptidase 4 (hDPP4), the receptor for MERS-CoV, and MERS-CoV Spike protein (MERS-CoV S) in mammalian cells and purified these proteins. The proteins were quantified with bicinchoninic acid protein assay (BCA), and the purities of each protein was evaluated with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Subsequently, the binding of hDPP4 and MERS-CoV S was verified using dynamic light scattering (DLS) which showed an increased hydrodynamic radius of the mixture of hDPP4 and MERS-CoV S compared to the measurements of the individual proteins in the control samples. Additionally, a direct ELISA indicated binding of hDPP4 to immobilized MERS-CoV S on a polystyrene 96-well microplate. We will discuss ongoing work, guided by these preliminary results, to develop an sVNT assay, which could be used to detect MERS-CoV RBD-targeting neutralizing antibodies in sera of immunized animals as well as in patient serum samples.